Sake Knowledge - A Lesson About Koji(-kin)

As I mentioned in the past two Newsletters - I will be in Osaka in February making sake at Daimon Shuzo for the Mukune International Sake Brewing Program. As the Director for this program I have been charged with crafting not only a great brewing experience, but also finding some field trips that shed further light on sake and sake making. Yasutaka Daimon mentioned a koji-kin making company in Osaka and we reached out about taking a tour of their facility. They agreed and we will get to see the "genesis" of the koji making experience.

As a primer Mr. Yamashita, the chief researcher of Higuchi Company - Koji mold makers - provided us with the following explanation of Koji and the Koji making process. I asked for permission to pass this on to the True Sake Newsletter readers and he heartily agreed. I did not edit or change his text.

The Japanese traditional fermentation foods are made by using koji. Koji molds grow in a variety of steamed grain and produce various enzymes. Koji is an enzyme preparation produced by growing mold such as Aspergillus oryzae on steamed cereals or pulses. Etymologically the word koji is an abbreviation of kabi-tachi meaning "bloom of mold"

The main role of Koji is analogous to the use of malt in Western nations. It supplies enzymes for degradation of materials in the fermentation process and produce liquid or paste-texture foods with a satisfying flavor and aroma, by the aid of yeast and lactic acid bacteria.

Historical documents suggest that the use of koji began more than 1600 years ago. At that time, koji making had originated in China and came to Japan via Korea. However from the early stages of koji making in Japan there were two differences to Chinese Koji- kernels of steamed cereals were used and the mold grown on them was mainly Aspergillus oryzae and Aspergillus sojae.

Initially koji starter was not used. The mold grown on the steamed cereals came naturally from the atmosphere. From experience the most suitable types of koji for fermentation products were discovered. Part of the previous batch of koji was kept and used as a starter for the next batch. This procedure continued for more than a thousand years until the early twentieth century without significant change, except for the addition of ash to promote growth, yield of conidia and durability.

At the beginning of Meiji period (1868-1912) , specialized producers started to supply koji starter to breweries on a commercial basis. However, the supply of purely cultured starter did not begin until the beginning of the twentieth century.

Koji starter production process

This is the process used in our company. Although other makers may have different procedures, in principle there are not many differences.

Ingredients 1-1 Medium
Lightly polished barley or rice is used for the koji mold culture medium. Light polishing facilitates the penetration of mycelia without losing too much of the cereal nutrients.

1-2 Nutrients
Ash of camellia is added to the cereals after steaming of materials to promote the growth and yield of conidia, and to advance durability.

1-3 Pure culture molds
We have hundreds of strains of Aspergillus. We incubate them on the steamed barley or rice adding potassium phosphate for five days. After drying for two days we collect durable conidia from each matured culture. We seal the conidia of each strain in screw vials and store them in a freezer at minus 20? for a few years to avoid mutation and to maintain viability without infection. The starters for the koji starter are cultured in pure form in flasks and dried. They are stored for use as the inoculum for kojt starter.

Production process2-1 Medium treatment and inoculation
Polished grain is washed, put into a rotary-type cooker and soaked in water for a few hours. The grain is then drained and allowed to stand for 10 hours, before pressure steaming for one hour. In order to obtain good yields of conidia and to increase their durability, potassium-phospate or ash is added as a nutrient. The steamed grain is cooled with filtrated air to avoid infection by alien microorganisms steamed After cooling one three thousandth of the starter for the koji starter is inoculated and the cooker is rotated to ensure uniform distribution of the conidia.

2-2 Incubation
First day: The inoculated grain is put into a cloth-lined crib and covered with canvas. It is wheeled into the pre-incubation room and incubated for 1 day at 30?.
Second day: The crib is brought into the incubation room. The grain is mixed thoroughly in the crib and transferred to Koji trays. About 1 kg of the grain is placed in a tray and spread evenly by hand. The tray is covered with damp cloth. The trays are then arranged in "brick lap stacks". Room temperature is controlled at 30? and humidity at 90-95%.
Third day: The cloths, which have dried by now, are replaced by new damp ones. The room conditions are as the day before.
Fourth day: The same as the third day.
Fifth day: Leave koji untouched until the next day.
Sixth day: The matured koji is removed from the incubation room.

Drying and Sieving3-1 Drying
The matured koji is transferred to square plates and spread out into a thin layer. The plate is placed on a trolley which is wheeled into a drying chamber where the koji is dried by titrated air at 40 degrees for 2 days.

3-2 Sievmq
By drying the water content of koji starter has become below 10% and the durability of koji starter has increased. The dried koji starter is then crushed and sifted to harvest conidia .

The conidia are separated from grain and hyphae by using net of two steps. The yields of conidia differ depending on the inoculated strain and incubation conditions. They range from 4 to 10 % of the weight of the initial raw material.

Production capacityWe can treat about 1 ton of raw materials per day. As I mentioned before, the yields of conidia differ according to the Aspergillus strains. Nevertheless, based on calculations from our annual data, we expect to get about 60kg per ton of raw material. Our factory operates six days a week for 49 weeks a year, giving us a production capacity of 17 tons of conidia in one year.

The annual output of conidia in Japan is estimated at 40 tons.

Our koji starter contain about 1010 cfu/ g of conidia and only less than 103cfu/g of bacteria. We are proud to their high purity.

ProductsNowadays we have many kinds of koji starters to cater for user's various needs.

Types

We are selling the koji starter differing three kinds of.

Grain type
This commodity is the most traditional form of koji starter. It consists of dried grain to which the conidia are still attached. It is usually used in the making of high-grade sake "ginjyo-shu" by traditional brewing methods.

Powder type This commodity consists of Aspergillus conidia and powdered potato or corn starch, because It becomes easy to use a small amount of conidia. Most products are of this type.

Meal type This commodity is made by crushing the whole grain koji starter, thereby guaranteeing even distribution of the conidia when you inoculate.

Explanation

As mentioned before, koji starter is used in the making of koji for the production of many kinds of Japanese fermented foods. We have a few hundred strains of Aspergillus. These strains have different properties to one another, for example enzyme production capacity ( balance, amount) , aroma of the matured koji, the appearance of mycelia (color, growth on the surface or in the grain) , growth(rate, affinity with the materials) etc.

We supply many kinds of koji starters to satisfy the needs of our customers. Normally we prepare ten kinds or more of koji starters to be used with one type of fermentation foods.